He looks the same, but doesn’t act the same, and Jerrel Jernigan laughs when he acknowledges his teammates probably see him nowadays and wonder, “Where did he come from?’’

That quiet, sometimes sullen player who rarely showed the speed he’s reputed to have and even less frequently looked as if he was having any fun? Gone, replaced by a happier, more confident version, arriving for work this spring “with a lot of swagger and stuff.’’

Swagger from Jerrel Jernigan?

“Haven’t felt that in a while, back to college,’’ Jernigan recently told The Post. “Before I was pretty much sweating through playing time here, playing time there, not really going out and loving football and having fun. Now it’s back to that point where I’m going out and having fun on the field, talking and joking with my teammates.’’

Some guys never seem to get any older. Jernigan turned 25 on Saturday and is about to enter his fourth year with the Giants.

Nearly three full seasons into his NFL career, Jernigan was traveling along the road marked “Draft Bust.” In his first 29 games for the Giants, the sum total of Jernigan’s contribution was negligible: 13 receptions, 114 yards, no touchdowns.

Jernigan celebrates his first career TD — against the Lions last December — with Hakeem Nicks.Photo: Getty Images

And then, as if awakened from a deep, deep sleep, in the last three games of last season, with the Giants’ dim playoff hopes all but snuffed out, Jernigan finally produced. Seven catches against the Seahawks, six against the Lions — plus his first career TD — and six more and another touchdown against the Redskins. It was more (19 receptions, 237 yards, two TDs) to show in three games than in the previous 29.

The late-season barrage was so startling, Giants co-owner John Mara, bitterly disappointed the day after the 7-9 season came to an end, openly questioned his coaching staff for keeping Jernigan so frequently on the bench.

“I’m not sure why it took us three years to find out that Jerrel Jernigan can play,’’ a frustrated Mara said. “We finally put him in the game and he starts making plays. Sometimes you have to put younger players in the game and give them a chance to fail or succeed. It would have been nice if he had gotten in a little bit earlier, but that’s not my decision.’’

Of all the players to single out, Jernigan may have been one of the most surprising choices.

“It meant a lot, that they’re actually paying attention and they know why they went out and drafted me and that I could go out and make plays, it was only a matter of time they put me out there,’’ Jernigan said of being singled out by Mara. “I just work here, I do what the coaches tell me to do and don’t complain, work hard every day and show ’em what I can do.

“It’s great [Mara] wants me out there and he wants to see me out there making plays.’’

Without those final three games, Jernigan might not have made it back for a fourth season with the Giants. He does not believe that to be the case, but nods in agreement that he needed something to jump-start his stalled career.

Jernigan speaks to the media after practice last week.Photo: Ron Antonelli

“I think I’d be back here right now trying to make the squad. I’d be on a tightrope right now,’’ Jernigan said. “No leeway to mess up. I still look at it as I’m on that tightrope, still got to go out and make plays because no spot is guaranteed out there, I got a lot of competition out there at the wideout position. Still got to show ’em what I can do so I can stay here.’’

Hakeem Nicks is gone (signed with the Colts) and Rueben Randle has moved into a starting role alongside Victor Cruz. Jernigan, though, might be stuck where he is on the depth chart, because the Giants selected a receiver, Odell Beckham Jr. from LSU, with the No. 12 overall pick in the NFL Draft, and the expectation is he will get on the field immediately.

“It didn’t bother me at all,’’ Jernigan said of the addition of Beckham. “Everyone knows we lost Hakeem Nicks, so we had to bring somebody else in.’’

Jernigan, at 5-foot-8 and 189 pounds, is well-suited to the slot receiver role, a spot Cruz is most effective in, causing a logjam. Beckham and Randle are considered more adept on the outside.

Jernigan will have to fight for playing time even after the three-game eruption that opened the eyes of the co-owner.